RE: [PATCH 0/2] introduce PM QoS interface

["Morten Brørup" <mb@smartsharesystems.com>]

> From: lihuisong (C) [mailto:lihuisong@huawei.com]
> Sent: Tuesday, 26 March 2024 03.12
> 
> 在 2024/3/22 20:35, Morten Brørup 写道:
> >> From: lihuisong (C) [mailto:lihuisong@huawei.com]
> >> Sent: Friday, 22 March 2024 09.54

[...]

> >> For the case need PM QoS in DPDK, I think, it is better to set cpu
> >> latency to zero to prevent service thread from the deeper the idle
> state.
> > It would defeat the purpose (i.e. not saving sufficient amounts of
> power) if the CPU cannot enter a deeper idle state.
> Yes, it is not good for power.
> AFAIS, PM QoS is just to decrease the influence for performance.
> Anyway, if we set to zero, system can be into Cstates-0 at least.
> >
> > Personally, I would think a wake-up latency of up to 10 microseconds
> should be fine for must purposes.
> > Default Linux timerslack is 50 microseconds, so you could also use
> that value.
> How much CPU latency is ok. Maybe, we can give the decision to the
> application.

Yes, the application should decide the acceptable worst-case latency.

> Linux will collect all these QoS request and use the minimum latency.
> what do you think, Morten?

For the example application, you could use a value of 50 microseconds and refer to this value also being the default timerslack in Linux.